| 摘要: | 自能源危機後，人們開始注重節約能源，因此增加建築物氣密性設計以減少室內與外氣空氣交換來降低能源消耗，但卻也使得室內空氣品質愈加惡化。應用非熱介電質放電(Dielectric Barrier Discharges，DBD)電漿系統來處理室內生物氣膠為一可行的辦法，但生物氣膠在受到電漿作用去除原有之生物性危害後，是否另產生具物理性危害之生物碎片微粒仍是值得關心探討的。因此本研究之目的是應用DBD非熱電漿系統結合濾材過濾單元來控制生物氣膠，期望未來能利用本研究發展之生物性空氣汙染物控制系統來改善室內空氣品質。
在非熱DBD電漿系統對生物氣膠之破壞去除方面，本研究使用霧化器產生生物氣膠後，調整相對濕度後進入電漿反應器停留1.5秒後，於電漿區出口處利用光學粒數偵測儀量測粒數濃度以評估電漿對生物氣膠控制之影響。實驗變因包含四種生物氣膠菌種：兩種細菌(大腸桿菌及枯草桿菌內孢子)及兩種真菌(酵母菌及青黴菌孢子)、放電電壓(0~19kV)、相對溼度(30%~70%)。
結果顯示放電電壓在15kV尚未產生電漿時，DBD電漿系統對於生物氣膠破壞去除效力大小為：青黴菌>酵母菌>枯草桿菌>大腸桿菌；不管是細胞型態(酵母菌>大腸桿菌)或是孢子型態（青黴菌>枯草桿菌)生物氣
膠，真菌種類之去除效果皆比細菌種類高。而當電壓≥16kV產生大量電漿後，產生之高能電漿對於四種生物氣膠具有相當高的破壞去除效率。此外，所有粒徑範圍下之生物氣膠皆會受到電漿作用而改變粒數分布，在高能電漿之破碎及分解作用下，大粒徑生物氣膠並不會轉移造成小粒徑生物氣膠之粒數濃度增加。增加放電電壓及相對濕度有助於提升DBD電漿對生物氣膠之破壞去除效力。
而DBD電漿結合濾材對生物氣膠過濾效率影響方面，經非熱DBD電漿處理後之帶負電荷大腸桿菌生物氣膠與帶正電纖維濾材因庫倫靜電力作用導致其比不帶電濾材具有較高的微粒收集效率。不帶電濾材對大腸桿菌生物氣膠之過濾效率具有隨放電電壓或相對濕度提升而提高之趨勢，然而帶靜電纖維濾材並無此類似趨勢。無論濾纖維材是否帶靜電，增加表面風速皆會減少次微米大腸桿菌生物氣膠與濾材接觸時間而降低濾材對生物氣膠之收集效率。以生物可培養計數方式量測到之生物氣膠過濾效率比光學方式量測之生物氣膠過濾效率來得高。
本研究系統在頻率60Hz、電壓17kV、相對濕度50%及停留時間1.5秒之最佳操作條件下，電漿對四種生物氣膠之去除效力均可達90%以上，而後端串接帶電纖維濾材單元於表面風速0.5m/s下，可進一步將非熱DBD電漿處理後殘存之氣膠量去除80%以上，電漿加濾材之結合系統對大腸桿菌生物氣膠整體去除效力高達98%以上，此結果顯示非熱DBD電漿系統結合濾材過濾單元對生物氣膠具有相當好的去除能力，是一有相當潛力應用於室內生物氣膠控制之方法。
People began to pay attention to energy conservation since energy crisis. The more airtight buildings were designed to reduce energy consumption by decreasing air exchange between indoor and outdoor. However, this kind design also makes the indoor air quality worsened. It still needed to explore whether the physical hazards of biofragments will be generated after removing the original bio-hazards of bioaerosols by plasma, although Dielectric Barrier Discharges (DBD) plasma system was a feasible method to control indoor bioaerosols. Therefore, the purpose of this study was to use the combination system of DBD non-thermal plasma system and filtration unit to control bioaerosols. It was expected that the combination system developed in this study could be applied to improve indoor air quality in the future.
For destroying bioaerosols using non-thermal DBD plasma, bioaerosols were generated by a nebulizer and then entered the plasma reactor with retention time of 1.5 sec after adjusting humidity. The particle number concentrations measured at the exit of plasma reactor by an optical particle counter were used to evaluate the effects of plasma on bioaerosols. The destroying efficacy of bioaerosols by plasma was evaluated based on different pivotal parameters including two types of bacterial bioaerosols (Escherichia coli and Bacillus subtilis endospore), two types of fungal bioaerosols (Candida famata var. flareri and Penicillium citrinum spore), applied voltages (0~19kV) and relative humidities (30%~70%).
When the plasma was still not generated at the applied voltage of 15kV, the destroying efficacy of bioaerosols by plasma system was following the order: P. citrinum>C. famata var. flareri>B. subtilis>E. Coli. It was found that the destroying efficacy of fungi with either non spore-form (C. famata var. flareri>E. Coli) or spore-form (P. citrinum>B. subtilis) was greater than that of bacteria. After the plasma generation at the applied voltages greater than or equal to 16kV, high-power plasma possessed high destroying efficacy to four different bioaerosols. Moreover, the bioaerosol number distributions were changed owing to the action of plasma in all size range of this study concerned. The decrease of amount of big size bioaerosols were not shifted to the increase of number concentrations of small size bioaerosols because of microorganismbreaking and decomposition by high-power plasma. Increasing applied voltage and relative humidity can promote DBD plasma to destroy bioaerosols.
For filtration efficiency of bioaerosols using combination system of DBD plasma and filter, the electret filter with positive charges was better than non-electret filter because of the interaction of electrostatic force between E. Coli bioaerosols with negative charges treated by DBD plasma and electret fibrous filter. The collection efficiency of E. Coli bioaerosols through non-electret filter increased with applied voltage or relative humidity, however, electret filter didn’t show the similar trend. Regardless of electret or non-electret fibrous filter, the filtration efficiency of E. Coli bioaerosols decreased with face velocity increased owing to the reduction of contact time between bioaerosols and fibers in filter. Compared with the optical particle counting method, the filtration efficiency measured by enumeration method for culturable E. Coli was higher.
For four different bioaerosols, the destroying efficacy by plasma were all greater than 90% at the optimal operation conditions of power frequency of 60Hz, applied voltage of 17kV, relative humidity of 50%, and retention time of 1.5 sec in this study. Higher than 80% of the residual E. Coli bioaerosols after non-thermal DBD plasma system treatment can be further removed by the following filtration unit with electret fibrous filter at the face velocity of 0.5 m/s. The overall removal efficacy of E. Coli bioaerosols was in excess of 98% using the combination system of plasma and filter. This research demonstrated the potential of combination system of non-thermal DBD plasma and filter to break down bioaerosols, and this system could be applied to improve indoor air quality. |
